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A very slow oscillation, real or apparent, of a satellite as viewed from the larger celestial body around which it revolves.

[Latin lībrātiō, lībrātiōn-, oscillation, from lībrātus, past participle of lībrāre, to balance, from lībra, balance.]

li′brate′ (lī′brāt′) v.
li·bra′tion·al adj.
li′bra·to′ry (-brə-tôr′ē) adj.


1. the act or an instance of oscillating
2. (Astronomy) a real or apparent oscillation of the moon enabling approximately 59 per cent of the surface to be visible from the earth over a period of time
[C17: from Latin librātus, from librāre to balance]
liˈbrational adj


(laɪˈbreɪ ʃən)

a real or apparent oscillatory motion, esp. of the moon.
[1595–1605; < Latin lībrātiō act of leveling = lībrā(re) to level, balance, derivative of lībra pair of scales + -tiō -tion]
li•bra′tion•al, adj.
li′bra•to`ry (-brəˌtɔr i, -ˌtoʊr i) adj.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.libration - (astronomy) a real or apparent slow oscillation of a moon or satellite; "the libration of the moon"
astronomy, uranology - the branch of physics that studies celestial bodies and the universe as a whole
variation - (astronomy) any perturbation of the mean motion or orbit of a planet or satellite (especially a perturbation of the earth's moon)
oscillation - the process of oscillating between states
References in periodicals archive ?
Diurnal libration, the third component, has nothing to do with the Moon itself.
Diurnal libration. You get a slightly different viewpoint toward the Moon depending on where you are on Earth's Moon-facing side.
Third (and least important) is diurnal libration. This time it's you, the observer, who does all the work.